Make --allow-dirty imply --allow-staged

[kornelski]

Staged changes don't really need protecting, and --allow-dirty is stronger than --allow-staged, so it can imply --allow-staged to make usage of cargo fix less verbose.

Closes #14176

[rustbot]

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[epage]

As a reminder, the Cargo team's policy is that Issues need to be S-accepted before moving onto PRs

[kornelski]

I don't know what else I can do to move the issue forward. My feature request hasn't been accepted nor rejected for months.